I. Field of the Invention
The present invention relates to an automatic wire bonder and more particularly to a bonding head for an automatic wire bonder of the type employed for aluminum wire wedge bonding.
II. Description of the Prior Art
Automatic wire bonders have been made which operate similar to numerical controlled machine tools. A semiconductor device to be wire bonded is placed in a working position on the wire bonding machine and a plurality of wires, each having first and second bond positions, are attached to the semiconductor device and/or the supporting substrate. A program is generated by a computer cooperating with servo devices as the first semiconductor is manually wire bonded. The program of the first bonding pattern is recorded and then may be employed to duplicate the same routine of wire bonds on other semiconductor devices. The process of generating the program is referred to as the learning mode or the teaching mode, implying that subsequent devices are bonded with the program which is now in a working mode. It is well known in the electronic data processing field that such programs may be stored in several types of memories and rapidly recalled and utilized through programmable electronic computing machines.
Prior art automatic wire bonders have employed an X-Y table which supported a work holder where the X-Y table was in turn supported on a theta or rotational drive table. The Z motion for the bonding tool was incorporated in a bonding tool actuating mechanism which was mounted on the machine frame opposite and apart from the work holder and the X-Y table. When the X-Y table and the drive motors are mounted atop the theta axis, the theta drive must be very heavy and require high torques to move the X-Y table and the work piece. Such an arrangement is inherently slow because of these large inertias; further, it comprises the design of the X-Y table.
Automatic wire bonders have been proposed which incorporate the mechanism for X-Y movement and rotational movement into a support mechanism for the bonding head. Here again when the theta drive is mounted on the X-Y motion mechanism there is a large amount of mass to be moved by the X-Y servos. In this type of arrangement the added mass of the bonding head is also moved by the X-Y servos and the theta or rotational bonding head drive motors. In this type device, the Z motion may be incorporated in the base for supporting the substrate or semiconductor device to avoid the necessity of the Z drive motor having to move the X-Y and theta mechanisms as well as the bonding head.
It is desirable to eliminate as much of the mass of the moving parts as possible. It is also desirable to reduce the setting time of vibrations so that the Z drive and theta drive servo mechanisms can drive the bonding tool to a bonding position as fast as the X-Y table can position the substrate opposite the bonding tool.
Heretofore, it was known that it was desirable to locate the working face of the bonding tool at the center of rotation of a rotatable bonding head in order to accurately position automatically the working face of the bonding tool over a desired bonding electrode or bonding pad. Heretofore automatic wire bonding machines having rotatable bonding heads having been plagued with the problem of accurately placing the working face of the bonding tool at the center of rotation of the rotatable bonding head. Prior art rotatable head wedge bonding machines have been provided with manual adjustable features to position the working face of the bonding tool at the center of rotation of the bonding head. It has been found that it is almost impossible to make such manual adjustments accurately. Further, it has been found that each time a bonding tool is replaced in the bonding tool holder the working face of the bonding tool is not repositioned in the exact position of the former tool. Thus, it has been found in the prior art that each time a bonding tool is replaced in the bonding tool holder that readjustment of the center of rotation of the working face of the bonding tool is required. Furthermore, it has been found that numerous prior art devices are not sufficiently accurate to maintain their center of rotation of the bonding tool at the same location.
It would be extremely desirable to provide an inexpensive, reliable, fast acting automatic wire bonding machine which would accurately locate the first and second bond positions after being taught or programmed where the location of the bonding pads are relative to the working face of the bonding tool.